Hydraulic axial piston machine



ocf. 29, 1963 K. BAUER HYDRAULIC AXIAL PISTON MACHINE Filed April l5, 1960 Fig.:

United States Patent O 3,108,545 HYDRAULIC AXlAL PSTON MACHINE Kari Bauer, Kainshacherstr. 2, Nurnberg- Laufamholz, Germany Filed Apr. 13, 1960, Ser. No. 22,041 Ciaims priority, application Germany Apr. 15, 1959 6 Claims. (ill. 10S-173) The present invention relates to a hydraulic axial piston machine `which may serve either as a pump or as a motor, in which the strokes of a plurality of pistons are produced either by mounting the cylinder block at a fixed angle or at an adjustable angle relative to the axis of the driving flange carrying the connecting rods of the pistons, or by reciprocating the pistons by means of a wobble plate which is mounted on the idnive shaft either at a fixed angle or at an adjustable angle relative to the axis 'of the cylinder block. The invention is further applicable to hydrostatic torque converters `and especially to those in which the pump and motor are mechanically connected to form a unit, in iwhich the driven shaft is mounted within the driving shaft, and the hydraulic pump and the hydraulic motor have a common valve plate and are mounted coaxially with the dri-ven shaft so as to act in opposite directions, and in which the strokes of the pistons are produced by wobble plates in such a manner that, when the speed ratio is 1: 1, no pumping action will take place, but only a coupling effect which is produced purely by `a hydrostatic-mechanical action, as described, for example, in my prior Patent No. 2,862,456.

In the prior art, various means have already been proposed for transmitting the strong piston forces'occurning during the operation under load to the wobble plate by means of the connecting-rod bearing ring. Thus, in modern hydraulic piston units various efforts have ybeen made to transmit the piston forces to the wobble :plate by hydrostatic means which are adapted to support these forces substantially free of any mechanical contact. This has been done by making the cross-sectional area of the hydraul-ic equipment acting upon the wobble plate slightly smaller than the cross-sectional area of Vthe piston cylinders so that the sealing contact surfaces would not separate from each other.

It is an object of the present invention to transmit the effective piston forces to the wobble plate likewise by hydrostatic means, namely, by transmitting the pressure contained in teach cylinder through a longitudinal bore in the connecting rod of the piston into a chamber which is located behind the ball-shaped head of each connecting rod and within the common bearing ring of all of the connecting rods. lt is then a further object of the invention to transmit the pressure from this chamber through a very small aperture, which produces a considera'ble throttling effect, into a cushioning chamber which acts upon the wobble plate. This cushioning chamber or pressure cushion is for-med by a recess in the bearing ring at the opposite side of each connecting rod ball head, and it is defined by the bottom and the side walls of the recess and yby a part of the surface of the wobble plate which is rotatable relative to the bearing ring. According to a further feature of the invention, this cushioning chamber or pressure cushion has an effective surface area which is considerably larger than the cross-sectional area of the working chamber in the associated cylinder and is, for example, 1.4 times `as large. Due to this pressure of the Ipressure cushion against the surface o-f the wobble plate, a marginal gap will be formed between the surface of the side walls of the recess and the surface of the wobble plate. Since at such a difference in size between the effective surface area of the pressure cushion and the cross-sectional area of the hydraulic working chamber of y 3,168,545@ Patented Oct. 29, 1$63 ice the associated cylinder, the pressure of the pressure cushion is slightly more than 70 percent of the pressure which prevails in the cylinder, the amount of oil which is released through the marginal gap of the pressure cushion will be exactly equal to the amount which is newly added through the throttling aperture. In this manuel' it is possible to transmit a piston force of any occurring strength hydrostatically to the wobble plate. The crosssectional size of the throttling. aperture and the viscosity of the pressure medium will then determine the average amount of leakage through the gap at a certain load upon the machine, and it will thus `also determine the medium width of the gap and consequently also the friction of the oil film within the gap. The amount of pressure oil required for continuously supplying a pressure cushion is therefore withdrawn from the working chamber of the associated cylinder, and the amount of oil thus removed is replenished in the usual manner at a low pressure by an oil pump at the suction side of the unit. v

A hydraulic cushion in cooperation with a throttling passage in front of this cushion can, however, properly produce the desired function as a hydrostatic transmission member between the bearing ring of the connecting rod and the wobble plate only if, as previously stated, the effective cross-sectional size o-f each pressure cushion is greater than the effective cross-sectional size of the associated cylinder. Each pressure cushion may according to the invention also :be divided into any desired number of partial pressure cushions, the total size of which is greater than the cross-sectional size of 4the working chamber of one cylinder. Although the mentioned ratio of 1.4:1 between the effective ycross-sectional size of a pressure cushion and that of the associated cylinder has been found to be very advantageous, the invention is by no means limited to such a ratio but this ratio may be varied considerably without seriously affecting the function of the apparatus.

Each hydraulic pressure cushion which is associated with one ofthe reciprocating pistons and acts upon the wobble disk is thus subjected to a pressure `generated therein which balances vthe force of the respective piston at both the suction and pressure strokes while maintaining a gap and thus a continuous coating of oil between the bearing ring of the connecting rods and the wobble disk. Thus, whenever the hydraulic machine operates under load, the 'bearing ring of the connecting rods will always be in a oating condition relative to the wobble plate. The length of time required for building up and releasing the pressure in a hydraulic pressure pocket in accordance with the change within the hydraulic working chamber `from the state of compression to the state of suction is extremely small and therefore of no effect upon the proper operation of the machine. The bearing ring of the connecting rods including the hydraulic pressure pockets therein which are subjected to a throttled pressure therefore forms together with the wobble plate a hydrostatic axial bearing which automatically adapts itself to the cccentnic load under any conditions occurring during the compression and suction strokes.

The advantage of transmitting the piston forces by means of such a hydrostatic axial bearing is that, despite the eccentric load and regardless of the strength of the load at any particular time, absolutely stable operating conditions will always be attained and a mechanical transmission of the piston forces will be absolutely avoided since by making `the throttling aperture of a suiiicient size, the width of the gap when the machine is under load may be made of such a size that, even though the relatively movable parts which slide along each other while floating on an intermediate oil coating might be subject to elastic deformation, a mechanical contact between these parts will never occur. Consequently, it is also no longer of any particular importance for the proper function of the machine if these parts have small surface irregularities and are not absolutely level and smooth. These parts therefore do not have to be made of such extreme accuracy and smoothness, and they-and especially the wobble platedo not have to be made of such a heavy construction to insure absolute rigidity as was required in previous apparatus of this kind.

In the accompanying drawings, in which only those parts of a preferred form of an axial piston machine are shown which are required to illustrate the present invention,

FIGURE l shows a longitudinal section of half of a hydrostatic torque converter forming the motor and having a nonrotating cylinder block; while FIGURE 2 shows a partial bottom view of the bearing ring of the piston connecting rods, as seen from a plane indicated by the Aline II-II of FIGURE l.

As illustrated in FIGURE l, the drive shaft 1 of the machine is rotatably mounted in a bearing plate 2 by means of a ball bearing 3, and in the stationary cylinder block 4 by a ball bearing 5. Wobble plate 6 is mounted on shaft 1 on a cross bolt 7 and pivotably adjustable to different angles by suitable means, not shown, which are known in the art and do not form a part of this invention. By these adjusting means it is thus possible, through bearing ring 8 of the connecting rods 9 of pistons 10, to adjust the length of the strokes of the individual pistons and thus to vary the delivery volumes of the pistons in the hydraulic working chambers 11 of the cylinders. Each connecting rod 9 is provided with a longitudinal bore 12 through which the working chamber 11 communicates with a chamber 13 at the lower side of the ball head 14 which forms the bearing member of connecting rod 9 and is mounted within bearing ring 8. This chamber 13 communicates through a small throttling aperture 15 in bearing ring 8 with a hydrailicpressure cushion 16 which is formed by a recess in the lower side of bearing ring 3 and the open, hydraulically active side of which faces toward the upper surface of wobble plate 6. By means of a threaded end ring 17 and an intermediate plate spring 18, bearing ring 8 is applied with a slight tension against wobble plate 6.

If, when the hydraulic machine is started, a pressure is produced in its cylinder rooms or chambers 11, this pressure will from each cylinder room 11 be transmitted through bore 12, chamber 13, and the throttling aperture 15 into the hydraulic pressure cushion 16. Since pressure cushion 16 has a larger cross-sectional area than working chamber 11, it will, as long as it contains a certain pressure mentioned below, be lifted from the surface of wobble plate 6, and to such an extent that a gap will be formed between the lower surface 19 of the narrow wall surrounding pressure cushion 16 and the surface of the wobble plate. This gap will at all times be of a size in accordance with the partial pressure contained in cushion 16 so that the amount of oil discharged from cushion 16 through this gap will correspond to the amount of oil entering into cushion 16 through the throttling aperture 15. This partial pressure in cushion 16 multiplied by the size of the effective cross-sectional area of the cushion is at any time in equilibrium with the force of the associated piston and thus balances that force. The gap between the surface 19 of the surrounding wall of pressure cushion 16 and the surface of wobble plate 6 is not shown in FIGURE 1 since it is too small to be indicated.

Although the effect of pressure cushion 16 together with vthat of throttling aperture and the gap between the .surrounding wall of the cushion and the surface of wobble plate 6 has been described specifically only with reference to one associated piston, the same effect will obviously be attained by the pressure cushions which are associated with the other pistons and all of which are similarly pro- `vided in the common bearing ring 8. Thus, the sum 0f the forces of all of the pistons will be transmitted entirely hydrOSaiCally t0 .wobble plate 6 and no mechanical '4 engagement of bearing ring 8 with the surface of wobble plate 6 will ever occur.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, I wish to have it understood that it is in no way limited to the details of such embodiment, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim l. In a hydraulic axial piston machine, in combination, a cylinder block having a cylinder means including a plurality of cylinders; piston means including a plurality of pistons respectively located in said cylinders and defining a plurality of cylinder chambers in the same, and a plurality of piston rods having first ends connected to said pistons and second ends having heads, each of said piston means having a conduit means connecting the respective cylinder chamber with said head of the respective piston rod; wobble plate means having a face; a bearing ring mounted on said wobble plate means and having a face confronting said face of said wobble plate means, said face of said bearing ring forming with said face of said wobble plate means a plurality of balancing chambers circumferentially spaced about said bearing ring, the crosssectional pressure area of each of said balancing charnbers being greater than the cross-sectional pressure area of the respective associated cylinder, said bearing ring having a plurality of bearing surfaces supporting said heads, and being formed with a plurality of throttling ducts opening on said bearing surfaces, respectively, and connecting said conduit means with said balancing chambers, respectively, so that the specific pressure in said balancing chambers is srnaller than the specific pressure in said cylinder chambers when the total pressure of said larger cross-sectional pressure area of said balancing chambers is in equilibrium with the total pressure of said cylinder chambers acting on said piston means whereby iluid continuously flows through said conduit means, said ducts, and said balancing chambers and is discharged between said faces whereby said faces are slightly separated and maintained parallel to each other while mechanical contact between said faces is prevented.

2. A hydraulic machine as set forth in claim l wherein each of said heads is ball-shaped and has a iiattened surface forming a space with the respective bearing surface, each duct connecting said space with the respective balancing chamber.

3. A hydraulic machine as set forth in claim 1 and including spring means for urging said bearing ring toward said face of said wobble plate so that said faces abut each other when the machine is not operated.

4. A hydraulic machine as set forth in claim 1 wherein said cross sectional pressure area of each of said balancing chambers is substantially 1.4 times the cross-sectional pressure area of the respective cylinder chamber.

5. In a hydraulic axial piston machine, in combination, a cylinder block having a cylinder means including a plurality of cylinders; piston means including a plurality of pistons respectively located in said cylinders and defining a plurality of cylinder chambers in the same, and a plurality of piston rods having first ends connected to said pistons and second ends having head, each of said piston means having a conduit means connecting the respective cylinder chamber with said head of the respective piston rod; wobble plate means having a face; a bearing ring mounted on said wobble plate means and having a face confronting said face of said wobble plate means, said face of said bearing ring being formed with a plurality of recesses circumferentially spaced about said bearing ring and forming with said face of said wobble plate means a plurality of balancing chambers, said bearing ring having on said face a plurality of annular projections respectively surrounding said recesses and having annular edge faces confronting said face of said wobble plate, the cross sectional pressure area of each of said balancing chambers being alessia greater than the cross-sectional pressure area of the respective associated cylinder, said bearing ring having a plurality of bearing surfaces supporting said heads, and being formed with a plurality of throttling ducts opening on said bearing surfaces, respectively, and connecting said conduit means with said balancing chambers, respectively, so that the specific pressure in said balancing chambers is smaller than the specific pressure in said cylinder chambers when the total pressure of said larger cross-sectional pressure area of said balancing chambers is in equilibrium with the total pressure of said cylinder chambers acting on said piston means whereby fluid continuously iiows through said conduit means, said ducts, and said balancing chambers and is discharged between said edge faces and said face of said wobble plate means whereby said edge faces are slightly separated by discharged iiuid from said face of said wobble plate means, the pressure acting in said circumferentially spaced balancing chambers maintaining said bearing ring in a position in which each of said annular edge faces is maintained parallel to said face of said wobble plate means whereby mechanical contact between portions of said edge faces and said face of said wobble plate means is prevented.

In a hydraulic axial piston machine, in combination, a cylinder block having a cylinder means including a plurality of cylinders; piston means including a plurality of pistons respectively located in said cylinders and deiining a plurality of cylinder chambers in the same, and a plurality of piston rods having lirst ends connected to said pistons and second ends having head, each of said piston means having a conduit means connecting the respective cylinder chamber with said head of the respective piston rod; wobble plate means having a face; a bearing ring mounted on said wobble plate means and having a face confronting said face of said wobble plate means, said face of Said bearing ring being formed with a plurality of recesses circumferentially spaced about said bearing ring and forming with said face of said wobble plate means a plurality of balancing chambers, said bearing ring having on said face a plurality of annular projections respectively surrounding said recesses and having annular edge faces confronting said face of said wobble plate, the cross sectional pressure area of each of said balancing chambers being greater than the cross-sectional pressure area of the respective associated cylinder, said bearing ring having a plurality of bearing surfaces supporting said heads, and being formed with a plurality of throttling ducts opening on said bearing surfaces, respectively, and connecting said conduit means with said balancing chambers, respectively, so that the specific pressure in said balancing chambers is smaller than the specific pressure in said cylinder chambers when the total pressure of said larger cross-sectional pressure area of said balancing chambers is in equilibrium with the total pressure of said cylinder chambers acting on said piston means wherebyfiuid continuously flows through said conduit means, said ducts, and said balancing chambers and is discharged between said edge faces and said face of said wobble plate means whereby said edge faces are slightly separated by discharged fluid from said face of said wobble plate means, the pressure acting in said circumferentially spaced balancing chambers maintaining said bearing ring in a position in which each of said annular edge faces is maintained parallel to said face of said wobble plate means whereby mechanical contact between portions of said edge faces and said face of said wobble plate means is prevented, said edge faces being planar and of uniform radial width, and said face of said wobble plate means having a planar face portions confronting, respectively, said planar edge faces in parallel relationship.

References Sited in the le of this patent UNITED STATES PATENTS 2,638,850 Ferris May 19, 1953 2,769,393 Cardillo, et al. Nov: 6*, 1956 2,821,932 Lucien Feb. 4, 1958` 2,862,456 Bauer Dec. y2, 1958 2,901,979 Henrichsen Sept/41, 1959 2,918,012 Lucien Dea-22, 1959 

1. IN A HYDRAULIC AXIAL PISTON MACHINE, IN COMBINATION, A CYLINDER BLOCK HAVING A CYLINDER MEANS INCLUDING A PLURALITY OF CYLINDERS; PISTON MEANS INCLUDING A PLURALITY OF PISTONS RESPECTIVELY LOCATED IN SAID CYLINDERS AND DEFINING A PLURALITY OF CYLINDER CHAMBERS IN THE SAME, AND A PLURALITY OF PISTON RODS HAVING FIRST ENDS CONNECTED TO SAID PISTONS AND SECOND ENDS HAVING HEADS, EACH OF SAID PISTON MEANS HAVING A CONDUIT MEANS CONNECTING THE RESPECTIVE CYLINDER CHAMBER WITH SAID HEAD OF THE RESPECTIVE PISTON ROD; WOBBLE PLATE MEANS HAVING A FACE; A BEARING RING MOUNTED ON SAID WOBBLE PLATE MEANS AND HAVING A FACE CONFRONTING SAID FACE OF SAID WOBBLE PLATE MEANS, SAID FACE OF SAID BEARING RING FORMING WITH SAID FACE OF SAID WOBBLE PLATE MEANS A PLURALITY OF A BALANCING CHAMBERS CIRCUMFERENTIALLY SPACED ABOUT SAID BEARING RING, THE CROSSSECTIONAL PRESSURE AREA OF EACH OF SAID BALANCING CHAMBERS BEING GREATER THAN THE CROSS-SECTIONAL PRESSURE AREA OF THE RESPECTIVE ASSOCIATED CYLINDER, SAID BEARING RING HAVING A PLURALITY OF BEARING SURFACES SUPPORTING SAID HEADS, AND BEING FORMED WITH A PLURALITY OF THROTTLING DUCTS OPENING ON SAID BEARING SURFACES, RESPECTIVELY, AND CONNECTING SAID CONDUIT MEANS WITH SAID BALANCING CHAMBERS, RESPECTIVELY SO THAT THE SPECIFIC PRESSURE IN SAID BALANCING CHAMBER IS SMALLER THAN THE SPECIFIC PRESSURE IN SAID CYLINDER CHAMBERS WHEN THE TOTAL PRESSURE OF SAID LARGER CROSS-SECTIONAL PRESSURE AREA OF SAID BALANCING CHAMBERS IS IN EQUILIBRIUM WITH THE TOTAL PRESSURE OF SAID CYLINDER CHAMBERS ACTING ON SAID PISTON MEANS WHEREBY FLUID CONTINUOUSLY FLOWS THROUGH SAID CONDUIT MEANS, SAID DUCTS, AND SAID BALANCING CHAMBERS AND IS DISCHARGED BETWEEN SAID FACES WHEREBY SAID FACES ARE SLIGHTLY SEPARATED AND MAINTAINED PARALLEL TO EACH OTHER WHILE MECHANICAL CONTACT BETWEEN SAID FACES IS PREVENTED. 